In a long term evolution (Long Term Evolution, LTE) system, a base station, which may be an eNB, uses a physical downlink control channel (Physical Downlink Control Channel, PDCCH) to transmit control signaling for scheduling a user equipment (User Equipment, UE), and when data of a UE in connected state is scheduled, the control signaling includes a cell radio network temporary identity (Cell Radio Network Temporary Identity, C-RNTI) of the UE, i.e., using C-RNTI of the UE to scramble, and the control signaling includes physical channel resource assigned for the UE and an adopted modulation and coding scheme (Modulation and Coding Scheme, MCS) and so forth. After receiving the control signaling transmitted on the PDCCH, the UE parses relevant information carried in the control signaling, and performs a sending and receiving of data on a corresponding physical channel according to indication thereof.
Control signaling transmitted on the PDCCH, per se, is also carried on certain physical resource for transmitting. Take a cell with a bandwidth of 5 MHz as an example, there are generally more than ten control signalings that may be carried in one transmission time interval (Transmission Time Interval, TTI) including both uplink and downlink scheduling signalings. As a result, when averaged to uplink or downlink, several to about ten users may be scheduled concurrently in one TTI. Further, in some scenarios, in a heterogeneous network for example, in order to reduce interference between cells, control signaling is probably sent only on some sub-frames. At the moment, number of control signalings transmitted on the PDCCH will be less. As the limited number of control signalings transmitted on PDCCH, number of users that may be scheduled is also limited.
In the prior art, a base station may trigger a UE served by the base station to initiate a random access procedure by sending a PDCCH order (Physical Downlink Control Channel order), wherein the PDCCH order is a kind of control signaling transmitted on the PDCCH. When the UE is in an uplink out-of-sync state, while at the moment, the base station has downlink data of the UE to transmit, the base station may firstly notify the UE by a PDCCH order to perform a random access to acquire uplink synchronization, and then performs downlink data transmission. In this case, after receiving the downlink data, the UE may send a hybrid automatic repeat request (Hybrid Automatic Repeat Request, HARQ) feedback, and a network side optimizes transmission manners according to the feedback.
When multiple UEs lose uplink synchronization, a base station needs the multiple UEs to re-acquire uplink synchronization by random access, and the base station needs to use PDCCH signaling to trigger the multiple UEs to perform random access, which will leads to a great amount of PDCCH signaling overhead.